Reconstructing past upwelling intensity and the seasonal dynamics of primary productivity along the Peruvian coastline from mollusk shell stable isotopes

Abstract

[1] We present here a potential new method to evaluate past variations of the mean intensity of Peruvian coastal upwelling and of the seasonal timing of phytoplankton blooms. This method uses a combination of the monthly carbon and oxygen isotopic signals preserved in fossil mollusk shells, and a series of corrections Copyright 2012 by the American Geophysical Union 1 of 17 to extract the variations of the dissolved inorganic carbon (DIC) d 13 C. Based on the analysis of five shell samples (85 shells in total) from the southern Peruvian coast, we suggest that the mean coastal upwelling intensity can be determined from a linear relationship between average values of corrected shell d 13 C and d 18 O. This new potential proxy would bring additional independent information valuable to interpret paleoproductivity changes reconstructed from marine sediment of the nearby continental shelf. Results obtained on fossil samples from the middle Holocene show an increase in upwelling intensity during this period associated to a spatial reorganization of upwelling centers along the South Peruvian coast. At the seasonal scale, corrected shell d 13 C enrichment indicates a phytoplankton bloom. Seasonal timing of phytoplankton blooms can be estimated by the lag with the annual temperature cycle reproduced by shell d 18 O monthly variations. The results obtained with two modern shell samples indicate phytoplankton blooms occurring during summer and fall, consistently with in situ productivity observations. Our method relies on revisited assumptions about the influence of temperature and metabolism in mollusk shell d 13 C. We further discussed the validity of these assumptions and the potential implications for the interpretation of similar data sets.

Coastal upwelling in Norway recorded in Great Scallop shells

“…Descriptions of fluctuations in upwelling have previously been made based on O and C isotopic analysis from modern marine mollusks like Mytilus californianus (Killingley and Berger 1979;Glassow et al 1994;Kennett et al 1997), Mesodesma donacium (Sadler et al 2012) or strombid snails (Wefer and Killingley 1980). The oxygen isotope ratio is known to be particularly sensitive to changes in water temperature and salinity and is preserved in calcareous fossils such as mollusk shells (Wefer and Berger 1991).…”

“…The CO 2 produced was enriched in 12 C and is preferred by the carbon anhydrase and incorporated into the calcite shell, impacting the shell's carbon isotope signals (McConnaughey et al 1997). Following these events, an enrichment of the d 13 C DIC signal can be attributed to preferential uptake of 12 C within the photic zone by phytoplankton during bloom events (Hellings et al 2000), increasing d 13 C shell and reflecting changes in marine productivity during upwelling events (Killingley and Berger 1979;Jones and Allmon 1995;Sadler et al 2012). Unlike these previous studies, the analyzed shells from Austevoll did not exhibit significant variations in d 13 C during the upwelling (Fig.…”

“…However, the main reason for the discrepancies between our investigation and previous research may be the brevity and intensity of the event analyzed here. Indeed, previous studies (Killingley and Berger 1979;Kennett et al 1997;Sadler et al 2012) analyzed mollusk shells collected in the most active and seasonal upwellings in California, Iberia/Canary and Humbold ecosystems (Chavez and Messi e 2009). Moreover, the incorporation time of carbon isotope signal in shells has been estimated of three to four days in Crassostrea gigas (Goodwin et al 2013) and more than one week for Ruditapes philippinarum (Poulain et al 2010) and for P. maximus (Marchais et al, unpubl).…”

Positive precipitation–evaporation budget from AD 460 to 1090 in the Saloum Delta (Senegal) indicated by mollusk oxygen isotopes

“…Mollusk shells have been shown to be faithful environmental archives (Goodwin et al, 2001;Carré et al, 2005;Schöne et al, 2005;Lazareth et al, 2006;Yamamoto et al, 2010;Batenburg et al, 2011;Carré et al, 2012a;Sadler et al, 2012).…”

El Niño Impact on Mollusk Biomineralization–Implications for Trace Element Proxy Reconstructions and the Paleo-Archeological Record

“…Many fossil shell accumulations are found in Pleistocene and Holocene coastal deposits as well as archeological sites [2]–[4], potentially extending reconstructions for past events. Isotope and radiocarbon data from bivalve shells have been used to characterize anomalies in sea surface temperature and upwelling triggered by El Niño [3], [5]–[7]. In contrast, trace element proxies (metal-to-calcium ratios [Me/Ca]) of bivalve shells have been scarcely explored for the characterization of El Niño events [4], [8], despite their usefulness in climatic and environmental studies [9]–[11].…”